A) increase
B) decrease
C) remain same
D) increase if the child is long and decrease if the child is short
Correct Answer: B
Solution :
Key Idea: When child stands up centre of mass shifts upwards. The child swings in simple harmonic motion, hence time-period is given by \[T=2\,\pi \sqrt{\frac{l}{g}}\] \[\Rightarrow \] \[T\propto \sqrt{l}\] where \[l\] is length of swing. When child stands up, the length is shortened as centre of mass shifts up, hence time period decreases.
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